Retaining ring for a chemical mechanical polishing tool

ABSTRACT

A retaining ring for a chemical mechanical polishing tool comprises a pad side surface. The pad side surface has an edge portion adjacent its outer circumference. A surface normal of the edge portion and a surface normal of the pad side surface include an acute angle. Additionally, or alternatively, the retaining ring may comprise at least one groove extending from an inner circumference of the pad side surface to the outer circumference of the pad side surface. The groove comprises at least one edge portion adjacent the pad side surface. A surface normal of the at least one edge portion and a surface normal of the pad side surface include an acute angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to the field of fabrication of integratedcircuits, and, more particularly, to a retaining ring for a chemicalmechanical polishing tool.

2. Description of the Related Art

In integrated circuits, a large number of circuit elements, such astransistors, capacitors and resistors, are fabricated on a singlesubstrate by depositing semiconductive, conductive and insulatingmaterial layers and patterning these layers by photolithography and etchtechniques. The individual circuit elements are electrically connectedby means of metal lines. In the formation of these metal lines, aso-called interlayer dielectric is deposited. Thereafter, vias andtrenches are formed in the interlayer dielectric. The vias and trenchesare then filled with a metal, e.g., copper, to provide electricalcontact between the circuit elements. In modern integrated circuits, aplurality of such metallization layers comprising metal lines arestacked on top of each other to maintain the required functionality. Therepeated patterning of material layers, however, creates a non-planarsurface topography, which may deteriorate subsequent patterningprocesses, especially for integrated circuits including features withminimum dimensions in the submicron range.

The surface of the substrate may be planarized between the formation ofsubsequent layers. A planar surface of the substrate is desirable forvarious reasons, one of them being the limited optical depth of focus inphotolithography which is used to pattern the material layers of microstructures. Chemical mechanical polishing is an appropriate and widelyused process to achieve global planarization of a substrate.

FIG. 1 shows a schematic sketch of a conventional chemical mechanicalpolishing tool 100. The chemical mechanical polishing tool 100 comprisesa platen 101 on which a polishing pad 102 is mounted. Frequently,polishing pads are formed of a cellular microstructure polymer materialhaving numerous voids, such as polyurethane. A polishing head 130comprises a body 104 and a substrate holder 105 for receiving andholding a substrate 103. The polishing head 130 is coupled to a driveassembly 106. The chemical mechanical polishing tool 100 furthercomprises a slurry supply 112 and a pad conditioner 131. The padconditioner 131 comprises a conditioning head 107 and a conditioning pad108 attached to the conditioning head 107. The conditioning head 107 iscoupled to a drive assembly 109.

A retaining ring 120 is attached to the body 104. The retaining ring 120has an inner diameter which is greater than the diameter of thesubstrate 103. Thus, the substrate 103 may be provided inside theretaining ring 120 such that the retaining ring 120 circumferentiallysurrounds the substrate 103.

In operation, the platen 101 rotates. The slurry supply 112 suppliesslurry to a surface of the polishing pad 102 where it is dispensed bycentrifugal forces. The slurry comprises a chemical compound reactingwith the material or materials on the surface of the substrate 103. Thereaction product is removed by abrasives contained in the slurry and/orthe polishing pad 102. The polishing head 130, and thus also thesubstrate 103, is rotated by the drive assembly 106 in order tosubstantially compensate for the effects of different angular velocitiesof parts of the polishing pad 102 at different radii. In advancedchemical mechanical polishing tools 100, the rotating polishing head 130is additionally moved across the polishing pad 102 to further optimizethe relative motion between the substrate 103 and the polishing pad 102and to maximize pad utilization. The drive assembly 109 rotates theconditioning head 107 and thus also the conditioning pad 108 attached toit. The conditioning pad 108 may comprise an abrasive component, e.g.,diamonds embedded in a matrix. Thus, the surface of the polishing pad102 is abraded and densified slurry, as well as particles that have beenpolished away from the surface of the substrate, are removed from voidsin the porous polishing pad 102. This process is denoted asconditioning.

Without conditioning, densified slurry and particles abraded from thesubstrate 103 might clog pores in the polishing pad 102. Thus, thepolishing pad 102 would lose its absorbency such that most of the slurrywould flow off the polishing pad 102 too quickly. Due to thisdegradation of the polishing pad 102, the removal rate in the polishingprocess would steadily decrease.

Conditioning may be performed after the polishing of one or moresubstrates 103. This, however, leads to significant variations of theremoval rate due to the difference between the reworked surface of afreshly conditioned polishing pad 102 compared to the exhausted surfacepresent immediately before the conditioning. Alternatively, the padconditioner 131 may be continuously in contact with the polishing pad102 while the substrate 103 is polished. Thus, a more uniform rate ofremoval of substrate material is achieved.

Various designs of chemical mechanical polishing devices are known inthe art. For example, the rotating platen 101 may be replaced with acontinuous belt kept in tension by rollers moving at high speed, orslurry may be injected through the polishing pad 102 in order to deliverslurry directly to the interface between the polishing pad 102 and thesubstrate 103.

In the operation of the chemical mechanical polishing tool 100, theretaining ring 120 may prevent or reduce the chance of the substrate 203becoming disengaged from the body 104 of the polishing head 130. In someexamples of chemical mechanical polishing tools 100 according to thestate of the art, the retaining ring 120 may contact the polishing pad102 during the chemical mechanical polishing process. In particular, theretaining ring 120 can be configured to exhibit a different pressure tothe polishing pad 102 than the substrate 103, for example a smallerpressure.

The pressure exhibited to the polishing pad 102 by the retaining ring120 may help to avoid an uneven distribution of pressure across thesurface of the substrate 103 which may occur in chemical mechanicalpolishing tools 100 wherein the retaining ring 120 does not contact thepolishing pad 102, and which may lead to different rates of materialremoval in portions of the substrate 103.

One problem of chemical mechanical polishing tools according to thestate of the art is that, during the polishing process, mechanicalfriction between the polishing pad 102 and the substrate 103 and/or theretaining ring 120 may induce moderately strong shear forces in thepolishing pad 102. The shear forces may be particularly high in chemicalmechanical polishing tools wherein the retaining ring 120 contacts thepolishing pad 102. Additionally, friction may lead to a reduction of thethickness of the polishing pad 102, due to an abrasion of the polishingpad 102, and to generation of frictional heat which may lead to anincrease of the temperature of the polishing pad 102.

The shear forces may be strong enough to create mechanical damage to thepolishing pad 102. Such damage may include rip out of the polishing pad102, holes in the polishing pad 102 and/or a local thinning of thepolishing pad 102. Damage to the polishing pad 102 may adversely affectthe substrate 103. For example, the substrate 103 may be scratched ormay even be broken.

A further problem of chemical mechanical tools according to the state ofthe art is that the retaining ring 120 may be ground during the chemicalmechanical polishing process. Thus, in the course of the operatinglifetime of the retaining ring 120, the retaining ring 120 may obtainsharp edges. The sharp edges may cut the polishing pad 102, thus leadingto damage to the polishing pad 102.

The present disclosure is directed to various methods and devices thatmay avoid, or at least reduce, the effects of one or more of theproblems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

According to one illustrative embodiment disclosed herein, a retainingring for a chemical mechanical polishing tool comprises a pad sidesurface having an edge portion adjacent an outer circumference thereof.A surface normal of the edge portion and a surface normal of the padside surface include an acute angle.

According to another illustrative embodiment disclosed herein, aretaining ring for a chemical mechanical polishing tool comprises a padside surface. The pad side surface comprises at least one grooveextending from an inner circumference of the pad side surface to anouter circumference of the pad side surface. The at least one groovecomprises at least one edge portion adjacent the pad side surface. Asurface normal of the at least one edge portion and a surface normal ofthe pad side surface include an acute angle.

According to yet another illustrative embodiment disclosed herein, amethod of chemical mechanical polishing comprises providing a retainingring comprising a pad side surface. The pad side surface comprises atleast one groove extending from an inner circumference of the pad sidesurface to an outer circumference of the pad side surface. The at leastone groove comprises an edge portion wherein a surface normal of theedge portion and a surface normal of the pad side surface include anacute angle. The retaining ring is rotated relative to a polishing pad.The direction of rotation is adapted such that the at least one groovemoves ahead of the edge portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 shows a schematic view of a chemical mechanical polishing toolaccording to the state of the art;

FIG. 2 a shows a schematic bottom view of a retaining ring according toan embodiment disclosed herein;

FIGS. 2 b and 2 c show schematic cross-sectional views of the retainingring shown in FIG. 2 a; and

FIGS. 3 a and 3 b show schematic cross-sectional views of a retainingring according to another embodiment disclosed herein.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Various illustrative embodiments of the invention are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

In one embodiment disclosed herein, a retaining ring for a chemicalmechanical polishing tool comprises an edge portion adjacent a pad sidesurface. In case the retaining ring is mounted in a chemical mechanicalpolishing tool, the pad side surface faces the polishing pad. The edgeportion may be provided at an outer or inner circumference of theretaining ring and/or may be provided at a groove formed in the pad sidesurface.

A surface normal of the edge portion and a surface normal of the padside surface include an acute angle. To this end, the edge portion mayhave a chamfered configuration or may be rounded. Thus, the occurrenceof sharp edges at the circumference of the retaining ring and/or thegrooved may be reduced or avoided. Even if the retaining ring is groundduring the course of the chemical mechanical polishing process, aportion of the edge in the vicinity of the surface of the polishing padhas an acute angle relative to the polishing pad surface. Therefore, asharpness of the edge may be reduced compared to retaining ringsaccording to the state of the art comprising edge portions which aresubstantially perpendicular to the pad side surface of the retainingring. Additionally, as the retaining ring moves across the surface ofthe polishing pad, the polishing pad may be guided by the edge portionsuch that the polishing pad slips smoothly under the retaining ring.This may help reducing friction between the retaining ring and thepolishing pad.

Thus, the subject matter disclosed herein reduces friction, which maylead to damage to the polishing pad and an undesirable increase of thetemperature of the polishing pad. Additionally, damage to the polishingpad resulting from the polishing pad being cut or ripped by sharp edgesof the retaining ring may be reduced.

FIG. 2 a shows a schematic bottom view of a retaining ring 200 accordingto one illustrative embodiment disclosed herein. The retaining ring 200may be adapted for use in a chemical mechanical polishing tool similarto the chemical mechanical polishing tool 100 described above withreference to FIG. 1. For example, the retaining ring 200 may be usedinstead of the retaining ring 120 according to the state of the artshown in FIG. 1.

The retaining ring 200 comprises a pad side surface 201 (see FIG. 2 b).In the operation of a chemical mechanical polishing tool comprising theretaining ring 200, the retaining ring 200 may be mounted such that thepad side surface 201 contacts a polishing pad of the chemical mechanicalpolishing tool. The retaining ring 200 may comprise a central opening223. In the operation of the chemical mechanical polishing tool, asubstrate holder similar to the substrate holder 105 described aboveand/or a substrate to be polished may be provided in the central opening223 such that the retaining ring 200 circumferentially surrounds thesubstrate to be polished.

In other embodiments, the retaining ring 200 may be formed integrallywith a substrate holder and/or a body of a polishing head. In suchembodiments, a recess adapted to receive the substrate to be polishedand/or a substrate holder may be provided instead of the central opening223.

The pad side surface 201 of the retaining ring 200 may comprise an edgeportion 202 which is provided adjacent an outer circumference of the padside surface 201, and may further comprise one or more grooves 203-210extending from an inner circumference of the pad side surface 201 to theouter circumference of the pad side surface 201.

FIG. 2 b shows a schematic cross-sectional view of the retaining ring200 along a plane 219 (FIG. 2 a) running through a center 224 of theretaining ring 200 and being substantially perpendicular to the plane ofdrawing of FIG. 2 a. The edge portion 202 of the retaining ring 200 maybe chamfered or rounded. Thus, the pad side surface 201 and the surfaceof the edge portion 202 may include an angle which is different from aright angle.

The relative orientation between the pad side surface 201 and thesurface of the edge portion 202 may be characterized by an angle 232between a surface normal 230 of the pad side surface 201 and a surfacenormal 231 of the edge portion 202.

As persons skilled in the art know, a surface normal of a surface is avector of unit length which is perpendicular to the surface, pointingaway from the surface. Thus, the surface normal 230 is perpendicular tothe pad side surface 201 and the surface normal 231 is perpendicular tothe surface of the edge portion 202. The surface normals 230, 231 pointaway from the retaining ring 200. The angle 232 may be an acute angle,having a value of less than 90 degrees. In some embodiments, the angle232 may have a value in a range from approximately 35-55 degrees.

FIG. 2 c shows a schematic cross-sectional view of the retaining ring200 along a plane 220 which runs through the groove 203 of the pad sidesurface 201 and is substantially perpendicular to a length direction ofthe groove 203 as well as to the plane of drawing of FIG. 2 a.

The groove 203 comprises a first edge portion 211 and a second edgeportion 225. The first edge portion 211 may be chamfered or rounded.Thus, a surface of the first edge portion 211 and the pad side surface201 may include an angle which is different from a right angle.

Similar to the edge portion 202 of the pad side surface 201, therelative orientation between the first edge portion 211 of the groove203 and the pad side surface 201 may be characterized by an angle 242between a surface normal 240 of the pad side surface 201 and a surfacenormal 241 of the first edge portion 211. The surface normal 241 issubstantially perpendicular to the surface of the edge portion 211,pointing away from the retaining ring 200.

The angle 242 may be an acute angle having a value less than 90 degrees.In some embodiments, the angle 242 may have a value in a range fromabout 35-55 degrees. In further embodiments, the angle 242 may besubstantially equal to the angle 232 (FIG. 2 b).

In one illustrative embodiment, the second edge portion 225 of thegroove 203 may be substantially perpendicular to the pad side surface201. Thus, a surface normal 250 of the pad side surface 201 and asurface normal 251 of the second edge portion 225 may be substantiallyperpendicular to each other.

In the operation of a chemical mechanical polishing tool comprising theretaining ring 200, the retaining ring 200 may be rotated in apredetermined direction of rotation, as indicated by arrow 222 in FIGS.2 a and 2 c. The direction of rotation 222 may be adapted such that thegroove 203 moves ahead of the first edge portion 211. The groove 203 maybe further angled forwardly in the direction of rotation 222. Slurrywhich is supplied to a polishing pad over which the retaining ring 200is rotated may pass through the groove 203, entering the central opening223 inside the retaining ring 200 to contact the semiconductor structureto be polished. The groove 203, when inclined forwardly in the directionof rotation, may advantageously improve an exchange of slurry betweenthe opening 223 and portions of the polishing pad outside the opening223 compared to a groove 203 being substantially radial or inclinedbackwardly.

The inclination of the groove 223 may be characterized by an angle 221(see FIG. 2 a) between the groove 203 and a radius 226 of the retainingring 200 running through an end 227 of the groove 223 at the innercircumference of the retaining ring 200. The angle 221 may have a valuegreater than zero. In some embodiments, the angle 221 may have a valuein a range from about 35-55 degrees, in particular a value of about 45degrees. The first edge portion 211 may be provided on a side of thegroove 203 which is nearer to the radius 226 than the second edgeportion 225 of the groove 203. Thus, the groove 203 can move ahead ofthe first edge portion 211 in case the retaining ring is rotated in thedirection of rotation 222 being adapted such that the groove 203 isinclined forwardly in the direction of rotation 222.

The other grooves 204-210 may have a configuration similar to that ofthe groove 203. In particular, each of the grooves 204 may comprise anedge portion wherein a surface normal of the edge portion and a surfacenormal of the pad side surface 201 include an acute angle. In FIG. 2 a,reference numeral 212 denotes an edge portion of the groove 204,reference numeral 213 denotes an edge portion of the groove 205, andreference numerals 214-218 denote edge portions of the grooves 206-210.

In the operation of the chemical mechanical polishing tool, theretaining ring 200 may be rotated relative to a polishing pad in thedirection of rotation 222. This can be done by rotating a polishing headto which the retaining ring 200 is attached, similar to the polishinghead 130 described above with reference to FIG. 1. Thereby, the pad sidesurface 201 may contact the polishing pad.

The edge portion 202 of the pad side surface 201 and the polishing padinclude an acute angle which is substantially equal to the angle 232.Thus, as the retaining ring 200 moves over the polishing pad, the edgeportion 202 may move over any unevenness of the polishing pad surface.Thus, the edge portion 202 and the pad side surface 201 may slide overthe unevenness rather than abut upon the unevenness. Thus, the edgeportion 202 may help reduce friction between the retaining ring 200 andthe polishing pad.

Furthermore, since the pad side surface 201 and the edge portion 202include an obtuse angle 270 at the interface between the pad sidesurface 201 and the edge portion 202, a formation of sharp edges may besubstantially avoided or at least reduced, even if the pad side surface201 is ground during the chemical mechanical polishing process.Therefore, a likelihood of damage to the polishing pad, such as cuttingand/or ripping the pad, may be advantageously reduced.

In embodiments wherein the pad side surface includes grooves 203-210,the edge portions 211-218 of the grooves 203-210 may help reducefriction between the polishing pad and the retaining ring 200 and mayfurther reduce a risk of damage to the polishing pad, similar to theedge portion 202 of the pad side surface 201.

The present invention is not restricted to embodiments wherein the edgeportion 202 of the pad side surface 201 and the edge portions 211-218 ofthe grooves 203-210 are chamfered. In other embodiments, some or all ofthe edge portions 202, 211-218 may be rounded.

FIG. 3 a shows a schematic cross-sectional view of the retaining ring200 along the plane 219 running through the center 224 of the retainingring 200 in an embodiment wherein the edge portion 202 of the pad sidesurface 201 is rounded. In FIG. 3 a, reference numeral 330 denotes asurface normal of the pad side surface 201 and reference numeral 331denotes a surface normal at a point 334 of the edge portion 202. Thesurface normals 330, 331 include an angle 332.

In embodiments wherein the edge portion 202 is rounded, the angle 332between the surface normal 330 of the pad side surface 201 and thesurface normal 331 of the edge portion 202 may depend on the location ofthe point 334. A surface normal of the edge portion 202 in the vicinityof the interface between the edge portion 202 and the pad side surface201 may have a smaller angle relative to the surface normal 330 than asurface normal of the edge portion 202 at a greater distance to theinterface between the edge portion 202 and the pad side surface 201.

The edge portion 202 may comprise at least one surface normal having anacute angle relative to the surface normal 330 of the pad side surface201. For example, the angle 332 between the surface normal 330 and thesurface normal 331 at the point 334 may have a value less than 90degrees. In some embodiments, the surface normal 330 of the pad sidesurface 201 and any surface normal at any point on the edge portion 202may include an acute angle.

In some embodiments, a cross-section of the edge portion 202 along aradial plane of the retaining ring 200 such as the plane 219 maycomprise a substantially elliptical arc section. In some embodiments,one of a major axis and a minor axis of the elliptical arc section maybe substantially parallel to the surface normal 330 of the pad sidesurface 330. Thus, a smooth transition between the pad side surface 201and the edge portion 202 may be provided. This may help to furtherreduce a likelihood of damage to the polishing pad when the retainingring 200 is used in a chemical mechanical polishing tool.

In further embodiments, a cross-section of the edge portion 202 along aradial plane of the retaining ring 200 may comprise a substantiallycircular arc section. In FIG. 3 a, reference numeral 333 denotes aradius of the arc section. The radius 333 may have a value in a rangefrom about 0.5-5 mm, in particular a value of about 2 mm.

In some embodiments, the edge portions 211-218 of the grooves 203-210may also have a rounded shape. FIG. 3 b shows a schematiccross-sectional view of the retaining ring 200 along the plane 220 insuch an embodiment. A surface normal 340 of the pad side surface 201 anda surface normal 341 of the first edge portion 211 of the groove 203 ata point 344 include an acute angle 342. Additionally, surface normals ata plurality of points at the edge portion 211 may include an acute anglewith the surface normal 340 of the pad side surface 201.

In some embodiments, a cross-section of the groove 203 along a planesubstantially perpendicular to a length direction of the groove 203 suchas the plane 203 may comprise a substantially elliptical arc section. Amajor axis of the elliptical arc section or a minor axis of theelliptical arc section may be substantially parallel to the surfacenormal 340 of the pad side surface 201. Thus, a smooth transitionbetween the pad side surface 201 and the first edge portion 211 of thegroove 203 may be provided, which may help to further reduce a risk ofthe polishing pad being damaged. In some embodiments, the first edgeportion 211 of the groove 203 may comprise a substantially circularcross-section having a radius 343. The radius 343 may have a value in arange from about 0.5-5 mm, in particular a value of about 2 mm.

The edge portions 212-218 of the other grooves 204-210 of the retainingring 200 may have a shape similar to that of the first edge portion 211of the groove 203.

The present invention is not restricted to embodiments wherein each ofthe grooves 203-210 comprises only one edge portion having a surfacenormal which includes an acute angle with a surface normal of the padside surface 201. In other embodiments, each of the grooves 203-211 maycomprise two edge portions wherein a surface normal of each edge portionand a surface normal of the pad side surface 201 include an acute angle.In some embodiments, each of the grooves 203-210 may comprise twochamfered edge portions. In other embodiments, each of the grooves203-210 may comprise two rounded edge portions wherein a cross-sectionof each edge portion perpendicular to a length direction of therespective groove 203-210 may comprise an elliptical and/or circular arcsection.

Advantageously, providing grooves comprising two edge portions whereineach edge portion has a surface normal including an acute angle with asurface normal of the pad side surface 201 may help reduce a likelihoodof damage to the polishing pad in case the direction of rotation of theretaining ring is reversed during the chemical mechanical polishingprocess.

Furthermore, the present invention is not restricted to embodimentswherein both edge portions of the grooves 203-210 and the edge portion202 of the pad side surface 201 comprise a surface normal including anacute angle with a surface normal of the pad side surface. In otherembodiments, one of the edge portions of the grooves 203-210 or the edgeportion 202 of the pad side surface 201 may be substantiallyperpendicular to the pad side surface.

Moreover, the number of grooves 203-210 of the retaining ring 200 neednot be eight, as shown in FIG. 2 a. In other embodiments, a differentnumber of grooves 203-210 may be provided. The number of grooves 203-210may be greater than eight or smaller than eight. In further embodiments,the grooves 203-210 may be omitted.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modifled andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

1. A retaining ring for a chemical mechanical polishing tool comprising a pad side surface, said pad side surface having an edge portion adjacent an outer circumference thereof, wherein a surface normal of said edge portion and a surface normal of said pad side surface include an acute angle.
 2. The retaining ring of claim 1, wherein said edge portion is chamfered.
 3. The retaining ring of claim 2, wherein said surface normal of said edge portion and said surface normal of said pad side surface include an angle in a range from about 35-55 degrees.
 4. The retaining ring of claim 1, wherein said edge portion has a rounded shape.
 5. The retaining ring of claim 4, wherein a cross-section of said edge portion along a radial plane comprises a substantially elliptical arc section.
 6. The retaining ring of claim 5, wherein said cross-section of said edge portion along said radial plane comprises a substantially circular arc section.
 7. The retaining ring of claim 6, wherein said substantially circular arc section has a radius in a range from about 0.5 mm to about 5 mm.
 8. The retaining ring of claim 1, wherein said pad side surface comprises at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said groove comprising at least one edge portion adjacent said pad side surface, wherein a surface normal of said at least one edge portion and a surface normal of said pad side surface include an acute angle.
 9. The retaining ring of claim 8, wherein said angle between said surface normal of said at least one edge portion of said groove and said pad side surface has a value in a range from about 35-55 degrees.
 10. A retaining ring for a chemical mechanical polishing tool comprising a pad side surface, wherein said pad side surface comprises at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said at least one groove comprising at least one edge portion adjacent said pad side surface, wherein a surface normal of said at least one edge portion and a surface normal of said pad side surface include an acute angle.
 11. The retaining ring of claim 10, wherein said at least one edge portion is chamfered.
 12. The retaining ring of claim 10, wherein said surface normal of said at least one edge portion and said surface normal of said pad side surface include an angle in a range from about 35-55 degrees.
 13. The retaining ring of claim 12, wherein said at least one edge portion is rounded.
 14. The retaining ring of claim 13, wherein a cross-section of said groove along a plane substantially perpendicular to a length direction of said groove comprise a substantially elliptical arc section.
 15. The retaining ring of claim 14, wherein said arc section is substantially circular.
 16. The retaining ring of claim 15, wherein said arc section has a radius in a range from about 0.5 mm to about 5 mm.
 17. The retaining ring of claim 10, wherein said at least one groove is inclined relative to a radius of said retaining ring running through an end of said groove at an inner circumference of said retaining ring, and wherein each of said grooves comprises one edge portion wherein a surface normal of said edge portion and said surface normal of said pad side surface include an acute angle, said edge portion being provided on a first side of said groove nearer to said radius than a second side of said groove.
 18. The retaining ring of claim 17, wherein a surface normal of another edge portion of said groove and said surface normal of said pad side surface are substantially perpendicular to each other.
 19. A chemical mechanical polishing tool, comprising: a retaining ring according to claim 17; and a drive unit adapted to rotate said retaining ring in a direction of rotation, wherein said direction of rotation is adapted such that said at least one groove is inclined forwardly in said direction of rotation.
 20. A method of chemical mechanical polishing, comprising: providing a retaining ring comprising a pad side surface, said pad side surface comprising at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said at least one groove comprising an edge portion, wherein a surface normal of said edge portion and a surface normal of said pad side surface include an acute angle; and rotating said retaining ring relative to a polishing pad in a direction of rotation, wherein said direction of rotation is adapted such that said at least one groove moves ahead of said edge. 